KDIGO (Kidney Disease: Improving Global Outcomes) is an international initiative whose guidelines set the modern classification of chronic kidney disease (CKD). The diagnosis is made if abnormalities of kidney structure or function persist for longer than three months. Severity is coded along two axes: the GFR category (G1–G5) and the albuminuria category (A1–A3).
Two axes and the cause (CGA)
The full KDIGO formulation includes three components — CGA: the cause of the disease (Cause), the GFR category (G) and the albuminuria category (A). GFR is calculated by the CKD-EPI formula based on creatinine (sometimes with cystatin C), and albuminuria — by the albumin-to-creatinine ratio (ACR) in urine. Two axes are needed because the kidneys can "leak" protein while filtration is still normal.
The risk map (heat map)
The combination of the G and A categories forms a colored "risk map": from green (low risk) through yellow and orange to red (very high risk). For example, G1A1 is low risk, while G4A3 is a very high risk of progression to kidney failure, cardiovascular events and death. Thus a single cell of the table shows both function and prognosis at once.
Why the classification is needed
The stage determines management: how often to monitor, when to refer to a nephrologist, which drugs to choose and which (nephrotoxic) ones to avoid. Early stages (G1–G2) are often asymptomatic and reversible with control of blood pressure, blood sugar and weight, so it is important to catch them on GFR screening rather than by complaints.
Reference ranges
KDIGO GFR categories (mL/min/1.73 m²):
| G1 | ≥ 90 — normal or high |
| G2 | 60–89 — mildly decreased |
| G3a | 45–59 — moderately decreased |
| G3b | 30–44 — substantially decreased |
| G4 | 15–29 — severely decreased |
| G5 | < 15 — kidney failure |
How the test is done
The G category is obtained from eGFR (CKD-EPI by creatinine and/or cystatin C), the A category from a morning urine sample (ACR). A single drop in GFR does not equal CKD: confirmation after ≥ 3 months is needed to distinguish a chronic condition from an acute one.
Calculate using this marker
Calculators where KDIGO is used directly:
Frequently asked questions
What does the entry "G3a A2" mean?
GFR 45–59 mL/min/1.73 m² (moderately decreased) combined with albuminuria of 30–300 mg/g. On the KDIGO risk map this is high risk: regular monitoring and protection of the kidneys and heart are needed.
Can a CKD stage be assigned from a single test?
No. First, the changes must persist for longer than three months — otherwise it may be an acute condition. Second, full classification requires both axes: GFR and albuminuria.